1. Field of the Invention
This invention relates to a compact, easy to use and portable smoke and clean air generating machine that enables the presence and location of leaks in a fluid system (e.g. the evaporative or brake system of a motor vehicle) to be accurately and visually detected depending upon the rate of air flow through the fluid system under test and whether smoke escapes from the system.
2. Background Art
Our patent application Ser. No. 09/020,841 filed Feb. 9, 1998 and entitled SMOKE PRODUCING APPARATUS FOR DETECTING LEAKS IN A FLUID SYSTEM discloses an efficient, portable apparatus for generating smoke in order to locate leaks in a fluid (e.g. air, oil, fuel, exhaust, etc.) system. A supply of oil within a sealed chamber is vaporized, and the resulting smoke is delivered to the system under test. By visually inspecting the system for smoke escaping therefrom, the precise location of a leak in the system can be accurately detected.
With the growing emphasis being placed on reducing the volume of emissions leaking into the atmosphere, it has become increasingly important to be able to monitor and test the integrity of a fuel vapor recovery or evaporative system in today""s motor vehicles. By way of example, to test for leaks, the evaporative system of a motor vehicle is typically pressurized for a predetermined time. If the pressure holds throughout the time interval, then the integrity of the system is presumed to be intact.
The problem is that this conventional method of testing for leaks in the vapor recovery system of a motor vehicle does not take into account the volume of fuel stored in the gas tank. That is to say, the smaller the volume of fuel stored in the gas tank, the greater will be the empty space within the tank lying above the fuel supply. Such empty space acts an air and pressure accumulator. More particularly, for a vehicle with less fuel and a larger air space in its tank, it will take a longer time to detect a leak. Therefore, the test operator can receive a false indication as to the integrity of the evaporative system, because of the increased time that is required for this system having an air accumulator to be fully pressurized. Consequently, an evaporative system which shows that it is holding pressure over time may actually have a leak and be in need of repair to avoid emissions to the atmosphere.
Accordingly, it is desirable to be able to overcome the aforementioned problems associated with the conventional method of testing for leaks in a fluid system so that the existence and location of a leak may be accurately verified and detected. To this end, it would also be desirable to achieve this goal by using the efficient smoke generating apparatus that is described in our above-entitled patent application.
Briefly, and in general terms, a smoke and clean air generating machine is disclosed that is adapted to produce either a supply of clean air or a supply of smoke to a fluid system (e.g. the evaporative or brake system of a motor vehicle) to be tested for leaks. An air compressor provides a supply of air under pressure. The air compressor is connected to supply air to a smoke generating apparatus or to a flow meter by means of a two-way bleed off selector valve. More particularly, with the selector valve rotated to a clean air position, the air compressor will communicate with the flow meter which measures the rate of air being delivered to the system under test. With the selector valve rotated to a smoke position, the air compressor will be connected to the smoke generating apparatus so that a supply of oil in a sealed chamber can be blown towards and vaporized by a heating grid and the resulting smoke delivered to the system under test. However, when the selector valve passes through a center position between its smoke position and clean air position, any pressure that has been developed in the air line between the air compressor and the smoke generating apparatus will be exhausted (i.e. bled off) to the atmosphere so as to automatically de-energize the heating grid of the smoke generating apparatus and thereby insure that the heating grid will cool and no additional smoke will be generated.
In operation, the selector valve is first rotated to its clean air position, whereby a supply of clean (i.e. non-smoky) air is delivered from the air compressor to the system under test via the flow meter. An air accumulator having an integral check valve to relieve excess pressure is located between the selector valve and the flow meter to smooth any pulsations in the flow of air to the meter. The existence of a leak having sufficient size to require repair is indicated in the event that the flow meter reads a rate of air flow from the air compressor to the system under test which is greater than a predetermined flow rate that is characteristic of a leak free system. Should a leak be indicated, the selector valve is then rotated to its smoke position, whereby a supply of air is delivered from the air compressor to the smoke generating apparatus. The smoke generating apparatus generates a supply of smoke via a smoke outlet line thereof to the fluid system under test. By visually inspecting the system under test for any escaping smoke, the precise location of a leak can be determined. Coupled to the smoke outlet line of the smoke generating apparatus is a pressure discharge accumulator having an integral check valve that is adapted to open to relieve excess pressure. In the event of a pressure build-up in the smoke outlet line (such as when the system to be tested is partially or completely restricted), the smoke is diverted to the check valve. As the exiting smoke begins to cool and condense, droplets of oil will be collected within the pressure discharge accumulator. The excess pressure within the smoke outlet line will then be dissipated to the atmosphere through a small orifice in the accumulator.
As an alternate embodiment of the present invention, the air compressor to deliver clean air to the flow meter and the smoke generating apparatus can be replaced by a pressure and flow regulated source of non-flammable nitrogen gas. In this case, a mixture of nitrogen (rather than air) and smoke will travel through the smoke outlet line to be delivered to the system under test so that a relatively safe, non-explosive environment can be established, particularly in situations characterized by high temperatures.